The present invention relates to a method of printing image frames from a digital image file of a motion picture.
Digital images have been printed onto a photosensitive medium using a liquid crystal display (LCD) as a modulator. The image presented on the LCD modulator is optically focused on the medium and a source or sources of light is allowed to illuminate the LCD modulator, which then creates a latent image on the medium. The wavelength of the light source needs to be carefully selected or tuned to match the spectral sensitivity of the medium in order to create an image with color and density as was intended by the data in the digital image file. When printing images on traditional color motion picture film, three primary sources of monochromatic red, green and blue light would be used to illuminate the LCD modulator to create the image. Each primary color corresponds to one of the three separable color records in the digital image data and color planes on the medium. For a single LCD modulator, each of the three separable planes on the medium would be exposed sequentially by the respective separable color records in the image file and the illumination source. The wavelength of these sources would generally be in the approximate range of 650 nm (red), 540 nm (green) and 450 nm (blue). For a monochromatic image only one image plane is on the medium, therefore only one of the three sources of light would be used to create the image. The choice of the illumination source wavelength would depend on the spectral sensitivity of the medium.
Digital motion picture image printers in use today uses a variety of technologies to perform the task. These systems employ technologies that are based on cathode ray tubes (CRT), raster scan laser beam and electron beam writing engines. These technologies as used in their current level of maturity are known to have inherent limitations. CRT systems such as that described in U.S. Pat. No. 4,754,334 are slow and generally do not have the capability to create images that make use of the full exposure range of the motion picture film because of the low radiance output of the CRT. It takes approximately 20 seconds to print a 2 k-resolution full aperture image using this system. The raster scan systems employs a spinning mirror called a scanner to impart motion to a focused modulated laser beam to expose and build the image one pixel at a time. A 2 k-resolution image can contain over 6 million pixels. The raster scan system may contain a single mirror or multi-mirror scanner. The limitations in such systems as described in U.S. Pat. No. 5,296,958 are due primarily to the limitations in speed of the scanner. The raster scan system is also relatively complex in its construction. It is estimated that the top end printing speed in a single beam, single scanner system is about 0.2 seconds per a 2 k-resolution image using current commercial components and technology. Electron beam systems are complex and the need to use special film types is a hindrance.
It is not practical to simply scale up these systems in order to gain speed. As an example, in order to print faster using a raster scan laser beam recorder, one could increase the speed of the scanner. Single mirror scanners (monogons) currently operate at approximately 65,000 RPMs, which is approximately the top end of their capabilities. Multi-mirror scanners (polygons) with 16 mirror facets are currently used today operating at approximately 6,500 RPM. In order to print faster, the scanners will have to operate at higher speeds but there are practical limitations relative to speed, the number of scanner mirrors, and the diameter of the scanner disk and cost. For example, the scanner motor loading varies as a function of the fifth power of the diameter and the square of the speed. It is possible to go faster but such an effort would result in added complexity, such as placing the scanner in a vacuum chamber to protect it and reduce drag. The power density of the writing spot may have to increase and the exposure time may have to decrease which could lead to reciprocity failures in the photosensitive medium.
A single two hour motion picture film sequence contains 172,800 high resolution discrete images. It is becoming common to see more motion picture films originating from digital sources. To this end, there is a need to be able to print these images in totality in a very short period of time to meet the needs of the digital mastering market. Using the best of the current technologies it would take approximately 192 hours to print these 2 k resolution images on 35 mm film using one machine. There is a need in the industry to reduce this time to less than 10 hours.
Two-dimensional spatial light modulators, such as those using a digital micromirror device (DMD) from Texas Instruments, Dallas, Tex., or using a liquid crystal display (LCD) from Victor Company of Japan, Limited (JVC) can be used to modulate an incoming optical beam for imaging. A spatial light modulator can be considered essentially as a two-dimensional array of light-valve elements, each element corresponding to an image pixel. Each array element is separately addressable and digitally controlled to modulate incident light from a light source by modulating the polarization state of the light. Polarization considerations are, therefore, important in the overall design of support optics for a spatial light modulator.
There are two basic types of LCD spatial light modulators currently in use, transmissive and reflective, respectively. Spatial light modulators have been developed and used for relatively low resolution applications such as digital projection systems and image display in portable devices such as TV and helmet display. Applications and teachings can be found in U.S. Pat. Nos. 5,325,137, 5,808,800, and 5,743,610. The requirements for projection and displays systems differs significantly from the requirements for high resolution printing to a photosensitive medium as would be required, for example, by the motion picture industry. The images from the first generation high resolution photosensitive medium will ultimately be used for creating a print film to be used for projection on a screen in a theatre. The process for creating the final projectable photosensitive medium would involve several generations of duplications and modifications by computer systems prior to the creation of the projectable medium. When viewing these intermediate high resolution photosensitive medium outputs or electronically scanning the original medium with a high resolution scanner, image artifacts, aberrations and nonuniformity will be more obvious. Optical systems for projectors and display applications are designed for the response of the human eye which, when viewing a display, is relatively insensitive to image artifacts, aberrations and nonuniformity, since the displayed image is continually refreshed and is viewed from a distance. Even more significant are differences in resolution requirements. Adapted for the human eye, projection and display systems are optimized for viewing at typical resolutions such as 72 dpi or less, but photographic printing used in the motion picture industry is generally printed at resolutions in excess of 1900 dpi. As a result of these requirements the optical, illumination, and image processing systems for a motion picture printer used in the motion picture industry can vary significantly from the aforementioned systems.
The current available resolution using digital micromirror device (DMD), as shown in U.S. Pat. Nos. 5,061,049 and 5,461,411 is not sufficient for the printing needs of the motion picture film industry and there is no clear technology path to increase the resolution. DMDs are expensive and not easily scaleable to higher resolution.
Low cost solutions using LCD modulators are described in U.S. Pat. Nos. 5,652,661, 5,701,185, and 5,745,156. Most involve the use of transmissive LCD modulators. While such a method offers several advantages in ease of optical design for printing, there are several drawbacks to the use of conventional transmissive LCD technology. Transmissive LCD modulators generally have reduced aperture ratios and the use of transmissive field-effect-transistors (TFT) on glass technology does not promote the pixel-to-pixel uniformity desired in many printing applications, especially that required in high resolution motion imaging. In order to provide high resolution, the transmissive LCD modulator""s footprint would have to be several inches in both dimensions, which would make the design of a practical output projection lens unreasonable in both cost and size. Transmissive LCD modulators are constrained to either low resolution and/or small images unsuitable for use in motion picture industry applications.
Another spatial light modulator that can be used is a single digital image light amplifier (SD-ILA) LCD. This device incorporates an integral RGB color separating holographic filter that focuses the RGB components of full white light spectrum of an illumination source onto RGB sub-pixels of each pixel in the modulator. Such a device is available from Victor Company of Japan, Limited (JVC). The apparent benefit of this device is the ability to use a single white light illumination source instead of RGB monochromatic color illumination sources to expose the medium and create an image. The problem with these devices in the motion picture printer application is that to obtain the needed high resolutions of 6 to 12 micrometer pixel pitch on 35 mm motion picture film, the LCD modulator would be relatively large. The design of the output projection lens would be costly and complex. Convergence of the three colors in a pixel would also be potentially a problem creating apparent and unacceptable color shifts and other artifacts in the image.
It is therefore an object of the present invention to provide an apparatus that minimizes the above noted problems while making use of commercially available elements.
It is another object of the present invention to make use of a reflective LCD modulator in the conversion of black and white and color digital images from a motion picture onto a photosensitive medium.
This object is achieved by a method of printing image records from a digital image file of a motion picture, comprising the steps of:
a) providing a two-dimensional LCD modulator having predetermined pixels which selectively can be activated so as respond to incident light to provide monochromatic visual images;
b) responding to the digital image file to manipulate the digital information contained therein to achieve desired effects in the images to be printed to the medium;
c) responding to the digital image file to activate the pixels in the display to sequentially illuminate the activated LCD modulator to provide visual image planes to provide images corresponding to each frame of the motion picture; and
d) moving a photosensitive medium past the display to illuminate different portions of such medium from the illuminated LCD modulator to record the image planes on such medium.
This object is further achieved by an apparatus for printing a plurality of frames wherein each such frame includes at least three separable color image records from a digital image file of a color motion picture, comprising the steps of:
a) means for receiving and storing the digital image file of the motion picture sequence;
b) an activatable two-dimensional reflective LCD modulator having predetermined pixels in which different colored monochromatic visual images corresponding to each motion picture frame can be produced;
c) means for activating the two-dimensional reflective LCD modulator in response to the digital image file so that reflective light will cause a visual image to be produced;
d) at least three arrays of spaced light-emitting diodes and each such array operates at a different color wavelength wherein each such color wavelength corresponds to an image plane;
e) an optical assembly for receiving light from each array and for distributing such light to provide a relatively uniform light beam;
f) a first polarizer responsive to the uniform light beam to polarize such uniform light beam;
g) a beam splitter for receiving the uniform polarized light beam and for directing a portion of the uniform polarized light beam onto the activated LCD modulator and for receiving and directing reflected light from the LCD modulator;
h) a second polarizer responsive to directed reflected light from the LCD modulator to minimize noise; and
i) means for moving a photosensitive medium past the reflective light produced by the second polarizer to illuminate such medium for a sufficient time with the visual image planes to record such image planes on such medium at proper exposure which matches the medium sensitivity.
The present invention is particularly suited for printing frames of either black and white or color motion pictures, such motion pictures can either be generated by a digital camera, scanned from images recorded on a photographic medium or can be computer generated digital images.
In the preferred embodiment of the invention, a reflective liquid crystal display can be effectively used to produce image frames. The present invention can make use of light-emitting diodes having particular wavelengths and an arrangement for using light produced by such arrays to efficiently illuminate the reflective LCD modulator.
The present invention using a reflective LCD modulator in a printer system offers some novel solutions to the current problems. It is known in the prior art that digital images residing on a computer can be decomposed into its representative color records and each color record can be written singularly to the LCD modulator. U.S. Pat. Nos. 6,016,157 and 5,970,215 use such a technique to create color prints using a single transmissive LCD modulator in a portable printer system. This invention works well in the particular applications where the need to print images do not exceed the limitations of the components and technologies. Specific limitations of the aforementioned patents would be the light energy needed to expose the photosensitive medium at very high speeds and the relatively low resolution of the transmissive LCD modulator. As is pointed out in the aforementioned patents, the object of the invention is aimed at a compact low energy battery powered system. Simply scaling up the system is not a practical solution to the speed problem, which would require major innovations in technology and designs yet to be developed.